The company I work for is close to being finished with our first web app and we recently made the decision to offer hosting for our smaller customers. (We provide software to lending companies and our larger customers are required to buy redundant servers to host their application). What we are trying to work out right now is how to create user generated subdomains that will hold a new instance of the software.

So a user will be able to sign up and say that the company name is XYZ Credit once they click on the create account button a url of xyzcredit.ourcompanyname.com is created and the user is redirected to it.

The servers that we want to use are running CentOS 5.5 and Virtualmin 3.83.